I have a few works in progress but as I worked on them I thought I could put together a few tutorials on what I've been doing. I'm a big fan of magnetizing weaponry on my models, you never know when you're going to want to swap out a weapon or two.
In this example I have magnetized a heavy stubber. The magnets I used for this project are the tiny 1/16 inch x 1/32 rare earth magnets from AmazingMagnets.com part #D032-063. They have great prices and an amazing selection of different shapes, sizes, finishes, and strengths. 100 of these magnets cost me less than $10.
Start by drilling out the hole on the interior of the stubber. It's almost already 1/16 inch but it will need to be opened up just a little to fit the magnet.
Cut off the post on the pintle which fits the same mounting hole which you just reamed out. After that, drill out the area where the post was with the same bit.
Drop a very small amount of superglue into each of the drill holes and sink the magnets. When placing the magnets make sure that the polarities are opposites, you don't want them repelling each other. I would also suggest that you always arrange your polarities in the same way. This way each model can swap weapons with the next. If you don't make this a standard in your models then there really is no sense in magnetizing at all.
Once this is done you will be able to add or remove the stubber as needed and swap out other weapons which you've magnetized, like a storm bolter or hunter killer.